1. Field of the Invention
This invention relates to a method of suppressing a background rise in a color reagent solution which is used to measure a component within a sample and which contains an oxidizing color reagent dissolved therein. The invention further relates to a color reagent solution which is used to measure a component within a sample and which contains an oxidizing color reagent dissolved therein, a reagent kit which includes such a color reagent solution, and a measuring apparatus which carries out measurement using such a reagent kit.
2. Description of the Related Art
It is generally held that about 2% of the oxygen consumed within an organism changes into reactive oxygen/free radicals. Here, “reactive oxygen/free radical” refers to a chemical species which is both reactive oxygen and a free radical. Most such reactive oxygen/free radicals are destroyed by the action of antioxidants and antioxidant enzymes; the reactive oxygen/free radicals that are not destroyed oxidize biological components such as DNA, lipids, enzymes and protein. It has been shown that oxidative damage to these biocomponents promotes aging and is also associated with the onset of diseases such as diabetes, high blood pressure and arteriosclerosis.
Here, the balance between reactive oxygen/free radicals on one hand and antioxidants and antioxidant enzymes on the other is referred to as the “oxidative stress.” The extent of such oxidative stress is referred to as the “degree of oxidative stress.” A “high oxidative stress” means that the balance within the organism between oxidizing effects by reactive oxygen/free radicals and antioxidizing effects by antioxidants and the like has broken down, resulting in state where there is a rise in oxidizing reactions. A state where the degree of oxidative stress is high is a state that is undesirable to the organism.
European Patent No. 0783692 B1, U.S. Pat. No. 6,355,489 B1 and Japanese Patent Application Laid-open No. 2009-257909 disclose methods for measuring the degree of oxidative stress. Components such as lipids, proteins, amino acids and nucleic acids within an organism incur oxidative reactions under the effect of reactive oxygen/free radicals, becoming hydroperoxides (R—OOH). These hydroperoxides are thus capable of serving as markers of the degree of oxidative stress. In the measurement methods described in these patent publications, the reactive oxygen/free radicals that arise within an organism are not directly measured; instead, the concentration of hydroperoxides within the blood that have formed under the action of the reactive oxygen/free radicals is measured using a color reaction, and the degree of oxidative stress within the organism is collectively assessed.
In the foregoing patent literature, p-phenylenediamine derivatives, which are oxidative color reagents, are used as the color reagents for such color reactions. These p-phenylenediamine derivatives are characterized by having a high sensitivity, and are useful as color reagents for use in measuring the concentration of such hydroperoxides.
However, there remains room for further improvement in the existing art.
That is, oxidative color reagents such as p-phenylenediamine derivatives are relatively unstable in a solution state and have a tendency to react with oxygen in the solution, as a result of which unintended coloration readily arises. On account of this, when stored in a solution state, a rise in the background occurs. One solution has been to, for example, freeze-dry the oxidative color reagent and store it as a dry reagent. This dry reagent is dissolved with a dissolving fluid at the time of use, and furnished for use. However, the need for such a pretreatment operation at the time of use is a burden on the operator who carries out the measurement. Hence, it would be desirable for the oxidative color reagent to be capable of being stored in a liquid state.